Summary of Work: Cobalt sulfate induced a higher incidence of alveolar/bronchiolar adenomas and carcinomas in male and female mice exposed to various concentrations of cobalt sulfate compared to controls. DNA samples from lung neoplasms were sequenced for point mutations in the K-ras gene. Unique point mutations were detected in K-ras exon 2. Future work on this project includes determining the mechanism for the unique mutations and characterizing genetic alterations in potential tumor suppressor genes which may be relevant to human exposure. The findings for the first part of these studies were printed in the NTP Review Board in December 1996.